Hi
I add a piece of code in multimedia.
It makes data in array reverse.
It works, but when I add -O2 or -O3 the result is error and vmov with -O2 ,-O3 create illegal instruction.
I don't understand...
Is this a gcc bug??
asm volatile
(
"pld [%0, #0xFFF];\n\t\
vldm %0!,{d0-d3};\n\t\
vswp.32 d0,d3;\n\t\
vswp.32 d1,d2;\n\t\
VREV64.32 q0, q0;\n\t\
VREV64.32 q1, q1;\n\t\
vstm %1!,{d0-d3};"
:
:"r"(data),"r"(coeff),"r"(tmp),"r"(sum),"r"(ptr)
:"d0", "d1","d2","d3","d4","d5","d6","d7"
);
vldm %1!,{d4-d7};\n\t\
VMUL.I32 d0,d0,d4;\n\t\
VMUL.I32 d1,d1,d5;\n\t\
VMUL.I32 d2,d2,d6;\n\t\
VMUL.I32 d3,d3,d7;\n\t\
VADD.I32 d0,d0,d1;\n\t\
VADD.I32 d2,d2,d3;\n\t\
VADD.I32 d0,d0,d2;\n\t\
VMOV %2,%3,d0;\n\t\
add %3,%3,%2;\n\t\
str %3,[%4]"
If your code is legal, I think this is an error in GCC.
My guess is that the optimizer might not recognize the instructions properly and thus might mess up the result.
I would recommend writing the assembly code in a separate file ending in .S, and then call it as a subroutine from C, when you need it.
-Eg. you would probably prefer a block of repeated assembly instructions / macros, so you don't have a small 'inner loop', which would waste time on branching / subroutine calling.
That would shield your code from the optimizer.
If you choose this solution, you can use the GNU Assembler's macros (.macro and .endm) and repeat code blocks using .rept and .endr...
Note: Although used by GCC, the GNU Assembler (GAS) is not a part of GCC; it's a completely different tool.